There are less and less Police HQs being built in city centres. This is a deliberate act on two fronts.
1. The cost of land in city centres.
2. Lessons learned during the Toxteth Riots in the 1980s when Merseyside Police HQ was within throwing distance.
Not only do you get a broken helicopter but several million pounds worth of building and equipment surrounding it.
I can't see why people are surprised about attacks on helicopters. Police vehicles have always been damaged when parked and unattended. It is merely the cost of repairs which has changed.